Today me and Koji set up the sensors to mesure the rhomboid motion as shown in the attachments.
We are using a fiber-coupled laser and a QPD. The QPD can be calibrated: we are going to determine the calibration curve to obtain the Volts/displacement ratio.
Attachment 1:scheme of the optics used.
Attachment 2, 3: picture of the system. We put an additional mirror on the rhomboid to balance the one we needed to sense motion.
We also put a mass on the bottom surface of the rhomboid to balance it.